I'd love to have a guest room, but we have a family of four in a three bedroom house. We looked at some 4 bedrooms, but none of them "fit" as well as the three bedroom did.
We have guests about 10 days a year. If it's my sister, one of the boys gives up his room, if it's my parents, we do. When dh's family comes there are a lot of people so we fit in wherever. We have a futon in the family room and some inflatable beds, so we always find a way.
I enjoy having a house where we use every square foot of it every day. I figure soon enough there will be empty rooms and I'll be missing these days!